deb <a href="http://security.debian.org">http://security.debian.org</a> stable/updates main contrib non-free /var/cache/apt This is where apt keeps the Packages.gz files and the actual packages which you tell it to download. there is a subdirectory called partial which is where interrupted or files which are currently being downloaded are kept. /var/lib/dpkg/info Where all debian package pre and post install and remove scripts are stored